The present invention relates generally to subsea production systems, and more particularly to subsea production systems having a bypass flow path from a point below a tubing hanger to a point above a tubing hanger.
Some subsea production systems have a wellhead located at the upper end of a well. The wellhead typically suspends one or more casing strings. Connected to the top of the wellhead is a tubing spool. A tubing hanger typically lands in the tubing spool, and the tubing hanger suspends a tubing string through the wellhead into the casing string. A conventional production tree can be connected to the top of the tubing spool. Conventional production trees include vertical and horizontal trees. Horizontal trees can be incorporated as part of the spool system. Vertical trees typically have a vertical passageway that receives an upward flow of product from the tubing hanger and a vertical passageway that receives an upward flow of annular fluid. Horizontal trees typically include a passageway that receives a vertical flow of product and one or more lateral passageways for delivering product and possibly annular fluid.
Production trees may include single or dual bore systems. A dual bore system permits the use of a production bore and a tubing annulus bore. Horizontal production trees typically have a production bore and a large diameter tubing hanger. Large diameter bores are difficult to seal in the presence of a high pressure, which results in large upthrust forces. To alleviate some of the problems associated with large diameter wells, wells have been drilled in two stages using a two stack system. For example, wells may be drilled with stacks having sizes of 18.75 inches and 13.625 inches. Vertical trees may also be used, but they typically include a top terminated annulus. Vertical production trees may be used to reduce the diameter of the tubing hanger. However, a reduction in the diameter of the tubing hanger reduces the diameter of tools that may enter the production system without removing the tree. Conventional production trees generally are not well suited for high pressure production systems having small spool and/or wellhead diameters.
During production it may be desirable to remove a production tree and replace it with a blow out preventer (“BOP”) and safely perform work over tasks. Alternatively, a BOP stack located on top of a tree may be used to work over a well. A BOP stack, however, typically exerts a large bending load to points at and below the point of connection of the BOP stack with the production system. Removing a conventional tree can be a time and labor consuming task that involves some risk of well destruction.